Will my wife's spousal benefits automatically change to full benefits at age 70 or does she need to contact social security in advance?
Hi. No, your wife can't be paid her own benefits until she applies for them. The only way that your wife could be collecting just spousal benefits only is if a) she was born prior to January 2 1954, b) she filed for spousal benefits at her full retirement age (FRA) or later, and c) she restricted her application for spousal benefits to exclude her own benefits from the scope of her application. Therefore, since your wife has apparently never applied for her own benefits she couldn't be paid those benefits unless and until she applies for them.
Social Security allows people to apply for benefits up to 4 months in advance of the month that they want to claim them, but you can also file as late as 6 months after the month you want to start your benefits if you're at least 6 months over FRA when you apply. So, if your wife wants to claim her benefits effective with the month she reaches age 70 she could file her application anytime from 4 months prior to that month to 6 months after that month.